Sorry for the slow reply, was out of town for the weekend and just didn't get around to it.
As for how I decide, currently I have it disabled at all times unless I need to get up to speed quickly or need to bring the SoC back up after a few FAS'd stop lights.
For the steeper hills, I think regen is the best bet. Maybe a pulse and glide kind of thing, but in reverse
if your SoC is low enough anyways. Though I believe that when using Regen, the car is also in fuel cut. Not 100% on that however.
As a side note, I managed to average 70mpg over the weekend, 210 miles. the last 60 miles or so it was tough to keep the FE gauge at 60ish mpg at 45-50mph(during the bad winds, otherwise 55-60), very bad head wind 30-40mph...
I believe that with the summer tires and summer fuel I will hit 80-90mpg over the same trip. Currently its winter RFG and Blizzak Snow tires.